As much as a wagon can carry. (Often used hyperbolically.)
1721. Cibber, Refusal, I. 1. Well, how goes Mississippi, man? What do they bring their money by waggon loads to market still?
1728. Young, Love Fame, I. 87. Imperious some a classic fame demand, For heaping up with a laborious hand, A waggon-load of meanings for one word.
1807. Farmers Mag., Nov., 471. A waggon-load [of wheat] is 12 or 14 barrels; each barrel 196 lib. weight.
1837. Dickens, Pickw., v. He wouldnt shy if he was to meet a vaggin-load of monkeys with their tails burnt off.
1855. Macaulay, Hist. Eng., xvii. IV. 66. He carries with him a waggonload of plate.
1913. J. G. Frazer, Golden Bough, VII. Balder, I. iv. 118. The butchers were rewarded with a waggon-load of wine.